This invention relates to a flame retardant product comprising a novel mixture of halogenated polyaromatic compounds having a low melting point range and the process therefor.
Mixtures of brominated non-condensed ring polyaromatics are known. For example, brominated diphenyl oxide mixtures having an average bromine number of from 7.0 to about 7.7 are sold commercially as flame retardants for use in thermoplastic formulations. These mixtures conventionally contain 0-2 weight percent hexabromodiphenyl oxide, 40-55 weight percent heptabromodiphenyl oxide, 30-40 weight percent octabromodiphenyl oxide, 5-15 weight percent nonabromodiphenyl oxide and 0-2 weight percent decabromodiphenyl oxide. Other brominated non-condensed ring polyaromatic mixtures are disclosed in: U.S. Pat . No. 3,833,674; U.S. Pat. No. 4,717,776; and U.S. Pat. No. 4,740,629.
The particular distribution of the various bromo homologs in the mixture will determine the mixture's average bromine number and its possible effect on the physical properties of articles made with thermoplastic formulations containing such mixtures. It is generally desirable to have a high average bromine number since the amount of bromine in the mixture is directly tied to the flame retardant effect per unit weight of the mixture in the formulation. Obtainment of high average bromine number has heretofore been accomplished by producing mixtures which contain large amounts of the hepta- and octabromo homologs. While these higher average bromine numbers are beneficial in regards to minimizing the amount of mixture needed to obtain a certain flame retardancy level, the use of large amounts of hepta- and octabromo homologs is not without a significant penalty. It has been found that suoh homologs contribute to a reduction in an articles, impact strength, which reduction is similar to that which occurs when a filler, e.g. talc, Mg(OH).sub.2, ZnO, etc. is present in the article. To give the mixture a less filler-type nature, the mixture should contain more of the less brominated homologs, e.g. the penta- and hexabromo homologs, and less of the hepta- and octabromo homologs. The lower brominated homologs, i.e. hexabromo and below, will give the mixture a plasticizer-type component which can be balanced against the filler-type component provided by the higher bromo homologs. A major problem with this approach is that the art has not developed a process which produces a mixture which contains significant amounts of the less brominated homologs and which, has, at the same time, a sufficiently high enough average bromine number. Generally, the mixture containing the less brominated homologs will also contain a higher amount of light-ends which is undesirable from the point of view of thermoplastic formulators.